The present invention relates to a magneto-conductive polymer composite and the process for the preparation of the same for read and write head for use in magnetic storage devices.
The present invention relates to a process for the preparation of magneto-conductive polymer composite comprising magnetic transition metal based alloy, a processable polymer capable of exhibiting magneto resistive properties and an additive to provide the conductivity property.
The embodiment of the invention resides in providing a method wherein the magnetic polymer composite is prepared having conductive as well as magnetic properties.
Prior Art
E. F. Fullerton, Applied Physics Letters, Vol. 63 (12), p. 1699-1701 (1993) teaches that conventional magnetoresistive materials like Permalloy have a positive MR ratio of a few percent while 150% magnetoresistance in sputtered Fe/Cr (100) superlattices.
P. M. Lev, in Science, Vol. 256, p.973,(1992) explains that high MR values at low temperature (typically below 50K) were also observed in Eu1-x GdxSe. Values of MR substantially larger (in absolute values) than those of the conventional materials are usually referred to as xe2x80x9cGiantxe2x80x9d MR.
K. Chahara et al. Applied Physics Letters, Vol.63 (14), pp.1990-1992, (1993) disclose a ratio of xe2x88x9253% in La0.72Ca0.25MnO3. The material exhibited essentially zero MR at room temperature. R. Von Helmholt et al. Physics. Review Letters, Vol. 71(14) pp. 2331-2333(1993) report the observation of a room temperature MR of xe2x88x92150% at room temperature, in thin films, the of (MR) material permalloy film which has a rate of change in resistance of perovskite-like La0.67Ca0.33MnO3. As deposited films were paramagnetic, but after subsequent heat treatment (900 C in air, 12 hrs) the samples exhibited a ferromagnetic magnetization curve. Bulk samples of that composition are known to be metallic ferromagnets, with Curie temperature of 343K, but small MR ratio.
Materials exhibiting magnetoresistive ratios greater than a few percent are useful in a variety of devices. Such devices utilize the resistive changes of the magnetoresistive materials, to the small changes in an applied magnetic field. This effect is useful in sensing devices, current sensing devices, memory elements and the like. U.S. Pat. Nos. 5,450,372 and 5,461,308 teach about the above mentioned useful device.
Although a Nixe2x80x94Fe alloy thin film (permalloy thin film) is conventionally used with a magnetoresistive ratio of 2 to 3%. To comply with the requirements to narrow the track of a magnetic head and increase the resolution of a magnetic sensor, a magnetoresistive material having a higher rate of change in resistance (MR ratio) is demanded. The phenomenon refered to as xe2x80x9cgiant magnetoresistive (GMR) effectxe2x80x9d has recently been found in Fe/Cr or Co/Cu multilayer thin films (refer to M. N. Baibich et al., Physical Review Letters, Vol. 61 (1988), p2472, D. H. Mosca et al., Journal of Magnetism and Magnetic Materials, Vol. 94 (1991), p L1). It is considered that, in such thin films, spin dependent scattering caused by conduction electrons located in the interface between Fe and Cr or Co and Cu contributes to the giant magnetoresistive effect. These films basically differ from conventional Nixe2x80x94Fe thin films in the generation mechanisim of the magnetoresistive effect. Although a MR ratio of 10% or more is obtained from these thin films, the need for the films to have a multi-layer structure complicates the fabrication process therefore.
A. E. Berkowitz et al., Pysical Review Letters, Vol. 68(1992), p3745, J. Q. Xiao et al., Physical Review Letters, Vol. 68(1992), p3749 indicates that magnetoresistive effect was observed in a single-layer thin film in which ultrafine Co, Fe or Ni grains (grain size: a few nm) are precitated in a Cu or Ag matrix.
Magnets are well known feature having a wide range of applications in using permanent (hard) or non-permanent magnets. The magneto resistive features are found mainly in two classes of compounds as ferromagnetic alloys and rare earth manganites. However, it has been observed that in both the cases, when the magnetic field is applied, there is remarkable drop in resistance. In the case of ferromagnetic alloys, the resistance varies with the thickness of the spacer and/or the non-magnetic layer, while in case of rare earth manganites, the resistance varies at the magnetic transition temperature. The ferromagnetic alloys in particular exhibit this behaviour when fabricated as multilayers with alternate stackings of magnetic and non-magnetic layers such as Fexe2x80x94Cr, Coxe2x80x94Cu, systems. The magnitude of magneto resistance varies as a function of layer thickness of Cr or Cu. However, magneto resistance in Agxe2x80x94Co system shows that the granular giant magneto-resistance is also observed wherein clusters of cobalt are dispersed in a non-magnetic matrix such as silver.
Electrically conducting polymer composite material exhibiting positive temperature coefficient of resistance is known in the art. However, polymer composite exhibiting both positive temperature coefficient of resistance and magneto-resistive effect is not known in the art. Hence, the conducting polymer composite materials consisting of a random distribution of a conducting filler throughout an insulating polymer are of interest for several applications.
Therefore there remains a need to have a material which exhibits higher MR at room temperature with increased device sensitivity, potential and enhanced reliability. It has been our object to provide a magneto-conductive polymer.
The object of the invention is to fabricate the magneto conductive polymer composite by isolating the components in the form of cones having effective coating of each particle of the magnetic alloys with the layer of polymer.
In the subject invention, the analogy of fabricating new systems wherein ferromagnetic compounds are dispersed in a non-magnetic, non-conducting polymer matrix have been developed by proper tailoring of the composite to aid percolation between such particles to obtain ferromagnetic behaviour in such composites.
The Cr is having anti-ferromagnetic property which brings about an anti-ferromagnetic coupling between Fe atoms, making Fexe2x80x94Cr alloys having magneto-resistive property resulting in the drop of Curie temperature of the Fe as an increase of the Cr doping. Such alloys can be used as conducting fillers in an insulating polymer matrix having electrical, magnetic and magneto-resistive behaviour.
The present invention is directed to a method for preparing polymer coated magnetic alloys preferably in the form of cones obtained by dissolving the processable polymer in a solvent and dispersing the alloy in the powder form by agitating the mixed polymeric solution and addition of an additive in the form of powder added to the said polymeric solution followed by solidification of the polymer coated alloy either in the form of a powder or as oriented cones.
The polymer of the subject invention to be coated on the magnetic alloy particles is vinyl-keto polymer. The subject polymer is selected due to its complete solubility in the solvent.
Accordingly, the subject invention relates to a magnetic polymer composite for read and write head for use in magnetic storage devices, comprising
60-90% by weight of the polymer preferably vinyl-keto polymer;
10-40% by weight of alloy preferably magneto-resistive alloys having magnetic properties; and
5-30% by weight of the additive preferably conducting carbon having conductivity properties.
The present invention also relates to a process for the preparation of a magnetic polymer composite, comprising
(a) dissolving the 60-90% by weight of the polymer preferably vinyl-keto polymer in a solvent by stirring the same in an open atmosphere at ambient temperature to obtain a clear, colourless solution;
(b) adding 10-40% by weight of alloy preferably magneto-resistive alloys in the said clear colour less solution;
(c) simultaneously adding 5-30% by weight of the additive preferably conducting carbon having conductivity properties in the said clear colour less solution
(d) agitating the said solution obtained from step (c) at frequency of 15-20 kHz for a period of 5-30 minutes, to get equally dispersed alloy in the said polymer solution;
(e) transferring the said polymer solution with equally dispersed said magneto-resistive alloys to the open non-metallic container on a magneto-stirrer allowing the said solvent to evaporate till the polymer coated transition metal based alloys are isolated in the form of cones from the said non-metallic container.
The said dissolution and mixing of the polymeric material results in effective coating of the said alloy particles.
The said agitation is done in a sonicator and the said non-metallic container is preferably a glass container.
The polymer coated transition metal based alloy isolated in the form of cones are having dimensions up to 1.5 mm-2.5 mm length and 0.4 mm-0.66 mm width.
The said polymer and magneto-resistive alloys are used in the powder form and the polymer used is polyvinylpyrrolidone and the said magneto-resistive alloys
The subject application may better be understood with reference to accompanying drawings. However, the same should not be construed to restrict the scope of the application as they are for illustrative purposes only.